The invention relates first of all to a hand-held hydraulic pressing apparatus with a hydraulic cylinder in which a hydraulically actuated piston can be displaced to carry out a pressing or cutting operation, with a piston head and a piston shank, the piston shank being connected to a tool carrier, and the tool carrier being part of an interchangeable apparatus head.
A hand-held pressing apparatus of this kind is known, for example, from DE-A1 197 16 804. This shows a hand-held pressing apparatus with a piston shank that can be screwed to the tool carrier of an interchangeable apparatus head and is formed in one piece with the hydraulically actuatable piston head.
With regard to the prior art described above, a technical problem for the invention is seen in further developing a hand-held hydraulic pressing apparatus of the type under discussion in an advantageous manner, particularly as regards making it simpler to change the apparatus head.
This problem is solved first and foremost by the subject-matter of claim 1, it being proposed that an interchangeable apparatus head should in each case have a piston shank with a return spring. In contrast to the known prior art, the piston shank in the configuration according to the invention is associated with the apparatus head. When the apparatus head is removed from the hand-held pressing apparatus, the tool carrier arranged displaceably in the apparatus head is always held in an initial position, i.e. in an open position, by the return spring which is also provided, this open position of the tool carrier corresponding, in the position in which the apparatus head is associated with the hand-held pressing apparatus, to the initial position, i.e. the returned position of the hydraulically actuatable piston or piston head. By virtue of this configuration, various interchangeable apparatus heads can be available in a stand-by position, i.e. in an open position, for fitting with pressing or cutting tools for example. It also proves advantageous here that once an interchangeable apparatus head formed in this way has been mounted on the hand-held pressing apparatus, the hydraulically actuatable piston or piston head is in its returned position, which can be defined as the initial position. By virtue of the configuration according to the invention, the apparatus head can be interchanged in an extremely simple manner. The cup- or disc-shaped piston head, which is provided with a hydraulic seal, for example in the form of an O-ring seal with a back-up ring, remains in the hydraulic cylinder on the apparatus. The piston shank, in contrast, is a separate component and, together with the return spring, is associated with the apparatus head. This advantageously allows the basic hand-held pressing apparatus to be preassembled, filled with oil and checked after repair work, for example. If required, a mating apparatus head is fitted. In the case of a repair, it is furthermore possible to exchange the apparatus head or basic apparatuses in a simple modular manner. Moreover, it is possible to change between pressing and cutting apparatus heads, for example, depending on the application, and, by virtue of the two-part nature of the piston, the exchange takes place on the dry side of the apparatus. The hydraulic side remains reliably closed by the piston head, which remains in the apparatus, thus eliminating the involved process of bleeding the system.
The invention furthermore relates to a hand-held pressing apparatus in accordance with the features of the precharacterizing clause of claim 1, where, as an advantageous refinement, the piston shank merely subjects the piston head to pressure without being connected to it. According to the invention, a two-part piston is provided here, having a piston head associated with the hand-held pressing apparatus and a piston shank associated with the apparatus head. The piston head, which is hydraulically pressurized when the apparatus is actuated, pushes the tool carrier via the piston shank, which is connected to the tool carrier, into the working position to press or cut objects. Upon manual actuation or automatic triggering when a predetermined pressure is exceeded, the piston shank together with the tool carrier moves back into the initial position, subjecting the piston head to pressure as it does so. This return movement is preferably brought about by a return spring acting on the piston shank. According to the invention, the piston shank and the piston head are not connected to one another, so that removing the apparatus head provided with the piston shank has no effect on the piston head. The latter always remains in its position, preferably in the returned position, to seal off the oil in contact with its rear side.
The invention also relates to a hand-held pressing apparatus in accordance with the features of the precharacterizing clause of claim 1, the proposal being made here, with a view to an advantageous further development, that the piston shank be connected to the piston head in a manner which allows it to be released in operation. In accordance with the previous embodiments, the piston is of two-part form in the case of this solution also, with a piston head associated with the basic hand-held pressing apparatus and a piston shank associated with the apparatus head. It is, for example, possible to provide here a releasable connection between piston shank and piston head which is accessible from the outside for removal of the apparatus head from the hand-held pressing apparatus. Possibilities that may be considered here are an axial screw connection or a bayonet connection between piston shank and piston head. This connection can be released to remove the apparatus head, after which the apparatus head can be removed in an extremely simple manner from the hand-held pressing apparatus. Here too, the sealing piston head remains in the basic apparatus.
The solutions described above can be used both separately and in combination.
Irrespective of the possible solutions described above, a further proposal is that a compression spring for returning the piston should be held captive on the piston shank. Even when the apparatus head has been removed from the apparatus, the piston shank is accordingly always loaded into an initial position-preferably an open position of the tools. Another provision is that the piston head has a centering recess or a centering projection on the piston-shank side and that the piston shank has a centering projection or a centering recess on the piston-head side. According to this configuration, the two parts of the two-part piston transmit only compressive and side forces to one another. The configuration according to the invention furthermore provides centering properties for the precise axial alignment of the piston shank. As an alternative to or in combination with this, provision can be made for a cylindrically-headed screw with a projecting cylindrical head to be mounted centrally in the piston shank on the piston-head side to ensure centering on the piston head, the cylindrical head being received in a corresponding recess in the piston head. As a further refinement of the subject-matter of the invention, provision is made for the return spring on the apparatus-head side to surround the piston shank and to be supported, at one end, on the apparatus head and, at the other end, on the piston shank in the region of the free end of the shank, which is associated with the piston head. For this purpose, a radial extension can be provided on the piston shank, which simultancously forms a centering projection. In a preferred configuration, the piston head on the apparatus is or disc-shaped form and has a radial scal. As an alternative, provision can also be made for the piston head to have a cup wall on the piston-shank side, the outside diameter of this cup wall being matched approximately to the inside diameter of the hydraulic cylinder. When the apparatus head and the hand-held pressing apparatus are coupled together, the cup wall accommodates the piston shank, if appropriate together with the return spring surrounding the shank. It has proven advantageous, particularly as regards the guiding properties of the piston head, for the height of the cup wall in the axial direction to correspond to more than a quarter of the length of the shank. The cup wall can furthermore also serve as an end stop in the course of the pressing operation, the annular end face of the cup wall engaging against a collar on the apparatus head, this collar projecting radially inwards into the path of motion As regards the fixing of the apparatus head on the basic apparatus, it is proposed that the hydraulic cylinder have an external thread on its end facing the apparatus head and that the apparatus head be connected to the hydraulic cylinder by means of this thread. As a result, the apparatus head can be unscrewed form the hand-held apparatus in an extremely simple manner while simultaneously pulling the piston shank out of the hydraulic cylinder together with the return spring, the piston head remaining in the basic apparatus maintaining its position. It has proven particularly advantageous here if the location of the connection between the apparatus head and the hydraulic cylinder is defined by an index pin. As a result of this, a defined connecting position is provided. When the predefined connecting position is reached, the index pin enters a recess in the hydraulic cylinder in a spring-assisted manner. According to a further proposal, the piston shank is of stepped form and is connected to the apparatus head by means of a counterholder component which is supported on the apparatus head and engages against the step face. This counterholder component on the one hand forms a stop face for the tool carrier. The return spring acting on the piston shank is preferably supported on the side opposite this stop face. This counterholder component is advantageously supported against a step on the apparatus-head side and can be inserted in an extremely simple manner. As an alternative, however, provision can also be made for the counterholder component to be screwed into the bore in the apparatus head which accommodates the hydraulic cylinder using the same thread for connecting the apparatus head to the hydraulic cylinder. A construction in which the apparatus head has a handle has proven particularly advantageous in terms of handling. This is furthermore preferably formed in such a way that the handle extends in the direction of motion of the piston or hydraulic cylinder. Finally, provision is made for the handle to be formed by an arc-shaped component which merges into the apparatus head at both ends.